Automation is used to increase the productivity of operators who perform order fulfillment. A category of automation termed “goods-to-operator” seeks to reduce the time that the operator spends moving to a location where the inventory item is for a pick by bringing the particular inventory item to the operator. Various carousel and mobile robotic approaches have been proposed for moving the inventory. Feedback to the operator via light or voice cues are also used to reduce the time required to pick. Similar techniques are generally known for replenishing inventory (“put operations”).